This project is an integrated, multidisciplinary effort to
understand variation in the life histories of temperate and tropical birds, and
thereby the diversification of life histories more generally. Although
differences in reproductive success and adult survival over latitudinal
gradients have attracted the attention of ecologists and evolutionary
biologists for more than 50 years, relatively little effort has been devoted to
the adaptive physiological and behavioral responses of birds to their environments
in a life-history context. Our project brings together a team of population
biologists and physiologists from a variety of disciplines to work together at
the intersection of environmental factors and physiological mechanisms that
influence demographic patterns of populations—what we refer to as the “life
history-physiology nexus.” The central prediction of the evolutionary theory of
life histories is that the balance between parental investment and
self-maintenance is related to annual adult survival rate. Furthermore,
adaptive responses of individuals and populations to their surroundings are
constrained. Time, resources, and body tissues are limited, and they must be
allocated optimally among different functions. Specific physiological
constraints on variation in life histories have received little attention but
may nonetheless shape life histories in significant ways. We propose to compare
small, altricial, terrestrial birds with varied life styles and living in
contrasting environments to address physiological and behavioral mechanisms
associated with variation in adult survival and related life-history variables.

understory
habitat along Pipeline Road, Panama

Objectives

This project will produce the most significant comparison to
date of physiology and behavior between tropical and temperate organisms. These
data will allow us to test a fundamental prediction of life history theory,
that the high adult survival rates and long breeding seasons typical of
tropical environments select for a slower pace of life, including reduced
reproductive investment and greater allocation of resources to adult
maintenance. In addition to comparing demographic components of life histories
in 10 phylogenetically matched pairs of tropical and temperate species,
individual components of the project will address different aspects of behavior
and physiology. These include activity and metabolic rate in the field and in
controlled environments, condition and health status, immune responses, stress
responses, and endocrine control mechanisms. Although the components of the
life history are complex, we expect to find correlated patterns among these
measurements that tie physiology and behavior to ecology and demography. These
patterns overlaid on an environmental and phylogenetic framework will provide
an integrated perspective on life-history evolution that includes physiological
mechanisms and constraints.

Integrated
nature of the project

The project directly involves eight senior personnel at
seven institutions. The participants are a mixture of established researchers
and new investigators, each of whom has an active research program that
addresses one or more components of the overall project, spanning
life-history theory, demographics, endocrinology, behavior, immunology, field
ecology, energetics, and aging. We also have a history of collaborative
research with each other. The University of Missouri-St. Louis will serve as
the lead institution for the grant, handling its financial aspects.
Twice-yearly coordinating meetings of the senior personnel will facilitate program
planning and the integration of projects. The investigators also will spend
substantial periods together in the field in Panama and Michigan.

This
large-scale study will be the first to synthesize demography and physiology in
order to characterize and interpret avian life histories. It will significantly
contribute to our understanding of avian longevity and life history adaptation,
and it will highlight species with contrasting life histories and physiological
makeup for future, more in-depth studies. Long-term benefits of this project
include the establishment of a lasting, multidisciplinary network of
collaborators, the development of a large, publicly available, comparative
database of behavioral and physiological information, and the training of a new
generation of biologists who are able to integrate disciplines crucial to
understanding the diversity of life.